Trailers are commonly utilized for a wide variety of towing and hauling purposes. Virtually all trailers are equipped with a standard set of rear lights, including turning, running (driving) and brake lights. Inspecting these lights is usually quite time consuming and annoying. In order for the rear lights and their associated wiring to be inspected, the trailer lighting circuit must be connected to a standard 12-volt battery. This is not a problem if the trailer is already hitched to the tow vehicle. However, in many cases, the inspection is performed without a connected tow vehicle, such as when the trailer is in a storage lot. In such circumstances, the battery first must be carried to the trailer. This is often quite cumbersome and inconvenient, particularly when a standard 12-volt automobile battery is used. Next, the inspector must connect the battery in turn to each light circuit of the trailer. After the proper connection is made, that person, or an assistant must walk to the rear of the trailer and determine whether the corresponding lights are operating properly. If the particular light or lights in question are not working, the inspector is still not able to determine the precise source of the problem. Light failure may be caused by a defective bulb, deteriorated wiring, a bad connection or a bad ground. The precise source of the difficulty must be investigated more fully. All of this testing and rewiring is very aggravating and time consuming. Oftentimes, it can require over 30 minutes to properly check the lighting for just a single trailer. If a number of trailers must be checked, the time, expense and manpower involved may be prohibitive.
Even when the trailer being inspected is already connected to an automobile, performing a check of the trailer's lighting circuit is often problematic. In such cases, the trailer lighting circuit is connected to the tow vehicle through a standard connecting plug. As a result, the person checking the lights does not have to connect the battery successively to each wire of the lighting circuit. However, checking the trailer lights can still constitute quite an annoyance. As each light is tested, the person conducting the inspection must either walk to the rear of the trailer or use an assistant. If a bad light is revealed, the automobile itself may be the source of the difficulty. Considerable time and effort are usually required to identify the precise source of the problem.